In a shrinking phase a transaction releases all locks

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- In a shrinking phase, a transaction releases all locks and cannot obtain any new locks. (iii) Assume that deadlock occurs. What techniques can be applied to control it? Please suggest one technique. - Deadlock prevention : a transaction requesting a new lock is aborted if there is a possibility that a deadlock can occur. - Deadlock detection : periodically test the database for deadlock. If it is found, one of the transactions is aborted and the other transaction continues. - Deadlock avoidance : the transaction must obtain all the locks it needs before it can be executed . 3. Describe the importance of concurrency control to a database management system. - Coordinating the simultaneous execution of transactions in a multiprocessing or multi-user database management system. - To ensure the serializability of transactions in a multi-user database management system. - It helps to guarantee data integrity and consistency in a database system. - If concurrency control is not maintained, three serious problems may be caused by concurrent transaction execution: lost updates, uncommitted data, and inconsistent retrievals. 4. Differentiate two types of locks, i.e. shared locks and exclusive locks. Shared locks are appropriate when concurrent transactions are granted READ access on the basis of a common lock, because concurrent transactions based on a READ cannot produce a conflict. Exclusive locks exist when access to a data item is specifically reserved for the transaction that locked the object. The exclusive lock must be used when a potential for conflict exists, e.g. when one or more transactions must update (WRITE) a data item. Exclusive lock is issued only when a transaction must WRITE (update) a data item and no locks are currently held on that data item by any other transaction. 5. ABC Markets sells products to customers. Unfortunately the database suddenly failed. Describe the techniques which ABC Markets may use in the database recovery process.
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  • Fall '19
  • Database management system, Database transaction

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